Why async move block is not needed?

[mkbanchi]

Looking at the very interesting crawler implementation in ch-05, i'm struggling with the fact that async block at crawler.rs:137 does not need to be move. queued_url is String that is not Copy so, even if it is cloneed inside the closure passed to for_each_concurrent, this should not suffice, it is borrowed inside the async block. I reprodued the problem with a similar (I think) example:

use futures::stream::StreamExt;
use tokio::sync::mpsc::{channel, Receiver, Sender};
use tokio_stream::wrappers::ReceiverStream;

#[tokio::main]
async fn main() {
    let v: Vec<String> = vec!["1".into(), "2".into(), "3".into()];

    let (tx, rx): (Sender<String>, Receiver<String>) = channel(3);

    let f = tokio::spawn(async move {
        ReceiverStream::new(rx)
            .for_each_concurrent(3, |val| {
                let val = val.clone();
                async {  // <-- This needs to be move
                    println!("Processed value: {}", val.clone());
                }
            })
            .await;
    });

    for i in v.iter() {
        tx.send(i.clone()).await.unwrap();
    }

    drop(tx);

    f.await.unwrap();

    println!("Finished");
}

The above code does not compile because of the missing move async block highlighted by the comment in the above snippet.